The vision of distribution optimization is to sustain the water quality leaving the plant throughout all points in the distribution system. To further define distribution system optimization, "optimization" refers to improving drinking water quality to the highest levels possible (which are normally above those required by EPA and Pennsylvania DEP regulations) to enhance public health protection without significant capital improvements to the water treatment plant or distribution system infrastructure.
Why Optimize?
The distribution system is the last "barrier" for protecting public health, meaning the physical and chemical barriers that have been established are necessary to protect the public from intentional or unintentional exposure to contaminants after the water has been treated.
Distribution system optimization focuses on two primary health concerns related to water quality within the distribution system:
- Microbial contamination
- Disinfection By-Product (DBP) formation
Microbial Contamination
Distribution systems have been implicated in a significant percentage of waterborne disease outbreaks, as seen in Figure 1. 1
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1 Centers for Disease Control and Prevention. (1991-2006). Surveillance for Waterborne Disease and Outbreaks Associated with Drinking Water and Water not Intended for Drinking. Morbidity and Mortality Weekly Report. Reports dated 1991-2006, as summarized by the US Environmental Protection Agency Technical Support Center, Cincinnati, OH.
These outbreaks are attributed to the breakdown in the distribution system physical or chemical barriers, or both. It is important to note that these statistics are based on reported outbreaks, which constitute two or more persons having been epidemiologically linked by location of exposure, time and illness. Many water-borne diseases may go untreated by a physician and are, therefore, unreported.
DBP Formation
The current regulated DBPs are Total Trihalomethanes (THMs), comprised of four species of trihalomethanes, and Haloacetic Acids (HAAs), comprised of five species of haloacetic acids. THMs and HAAs are, simply stated, a product of a reaction between a disinfectant (chlorine or monochloramine) and precursors (natural organic matter and bromide). The overall formation is affected by various parameters including concentration of precursors, disinfectant dose and residual, time, temperature and pH. Potential DBP related health concerns include suspected carcinogens (bladder cancer) and reproductive and developmental disorders.
Distribution system optimization will lead to increased public health protection through increased monitoring and operational oversight, resulting in improved physical protection and improved water quality for all customers.